Ion Mobility Separation or Spectrometry (“IMS”) is a well established analytical technique whereby ions are separated according to their ion mobility by subjecting the ions to a weak electric field in the presence of a buffer gas. The ions experience a force in one direction due to the electric field and an effective force in the opposite direction due to collisions with the buffer gas.
At low electric fields, the ion mobility of a given ion, K, can be calculated approximately with the equation:
                    K        =                              3            16                    ⁢                                                    2                ⁢                                                                  ⁢                π                                            μ                ⁢                                                                  ⁢                kT                                              ⁢                      Q                          n              ⁢                                                          ⁢              σ                                                          (        1        )            wherein Q is the ion charge, n is the buffer gas number density, p is the reduced mass of the ion and the buffer gas molecules, k is Boltzmann constant, T is the buffer gas temperature and a is the collision cross section (“CCS”) of the ion.
When coupling an ion mobility separator to a mass spectrometer or filter (“MS”) and/or other analytical devices, it is generally preferable to locate the ion mobility separator between the ion source and the mass spectrometer. This is particularly true when using an ion source that operates at or close to atmospheric pressure, as the operating pressures of typical ion mobility separators fall between atmospheric pressure and the operating pressure of many mass spectrometers.
While this approach is advantageous, e.g. from a cost perspective, it can lead to problems in the accuracy and precision of ion mobility and/or collision cross section measurements, since variations in the ambient (external) or ion source environment can directly influence the internal environment of the ion mobility separator. For example, changes in the ambient environment due to liquid chromatography (“LC”) gradient changes, changes in sample or matrix flow rates, and changes in source gas flows rates can all affect the internal ion mobility separator environment.
These effects are typically avoided or reduced by introducing one or more differential pumping stages between the ion source and the ion mobility separator, and re-filling the ion mobility separator with a buffer gas. However, this adds additional cost and complexity to the system.
US 2002/0014586 (Clemmer) discloses with relation to FIG. 5 an IMS arrangement in which a buffer gas is regulated by buffer gas source 46 and a pump 80.
WO 2013/080044 (Hart) discloses a FAIMS system in which temperature and pressure sensors are used to monitor the FAIMS core. Pressure correction is achieved by adjusting the FAIMS scan parameters based on measurements from these sensors.
US 2005/0092918 (Smith) discloses an IMS arrangement in which a buffer gas supplied via lines is regulated using a pressure sensor and a flow regulator.
WO 2010/125357 (Giles) discloses a differential mobility spectrometry (DMS) device arranged in a pressured controlled vacuum chamber.
US 2011/0183431 (Covey) discloses a differential mobility spectrometry (DMS) device arranged in a temperature regulated vacuum chamber.
EP-1562040 (Guevremont) discloses a FAIMS device having a temperature sensor and a temperature controller.
U.S. Pat. No. 5,796,099 (Jackson) discloses an ion mobility spectrometer whose calibration is corrected based on the operating pressure and temperature.
U.S. Pat. No. 5,736,739 (Uber) discloses an IMS device having flow sensors and flow adjustment valves.
EP-2613140 (Sato) discloses an IMS device having a mass flow controller.
It is desired to provide an improved mass spectrometer and an improved method of mass spectrometry.